1. Field of the Invention
The present invention relates to an inline vacuum processing apparatus for manufacturing an information recording disk having a carbon protective film on a magnetic film serving as a recording layer, a method of controlling the same, and an information recording medium manufacturing method.
2. Description of the Related Art
A magnetic recording disk such as a hard disk is formed by sequentially stacking, on the upper surface or both of the upper and lower surfaces of, e.g., an aluminum or glass substrate, a metal underlying film made of Cr or the like, a magnetic recording film made of CoCrTa or the like, and a protective film made of a carbon film or the like to protect the magnetic recording film from corrosion caused by contact with a magnetic head or air.
The carbon film was conventionally formed by sputtering deposition. However, the rising recording density is requiring the carbon protective film to be thinner and have necessary durability. Plasma CVD is used nowadays because it can form a very hard and thin, carbon protective film (Diamond-Like Carbon: DLC).
A general plasma CVD apparatus includes a chamber capable of forming a vacuum inside, and a pair of parallel plate electrodes installed in the chamber. A substrate is placed on the grounded anode. In this state, a reaction gas such as CH4 or C6H5CH3 containing carbon is introduced into the chamber. A voltage is applied between the electrodes to generate a plasma, thereby depositing a carbon film on the substrate surface.
However, plasma CVD deposits the carbon film not only on the substrate surface but also around it, i.e., on the exposed inner surface of the chamber. As the carbon film formation on a substrate is repeated, the carbon film deposited on the inner surface of the chamber gradually thickens unless the formed carbon film is removed each time. The carbon film deposited inside the chamber peels off in time due to internal stress or the like and generates carbon particles.
In manufacturing a magnetic recording disk, to improve the productivity, there is a demand for omitting a process that is not directly relevant to the manufacture such as a process of removing the carbon film deposited inside the plasma CVD chamber. This need is especially strong for a so-called inline information disk forming apparatus formed by endlessly connecting, in a line, a plurality of chambers to be used for thin film formation and processing.
In a magnetic information disk forming apparatus, every time a process of a chamber in the production line has ended, the carrier is sequentially moved to the adjacent chamber so that the next process is executed for the substrate on the carrier. Each chamber is designed to perform a process for a substrate held on each carrier. The overall production efficiency of the production line is therefore decided by the most time-consuming one of the processes in the chambers.
In magnetic recording disk forming, normally, carbon protective film formation by plasma CVD is the most time-consuming process. Hence, executing not only the most time-consuming process for forming a carbon protective film by plasma CVD but also a process of removing the carbon film inside the chamber lowers the productivity of the entire production line. There is a demand for minimizing the decrease of the productivity.
However, without carbon film removal, particles generated upon peeling off the carbon film stick to the substrate surface to form projections on the surface of the carbon film formed on the substrate (cause local film thickness abnormality). These projections pose a problem in a lubricant layer formation process later and also become a cause of defectives.
A conventional information recording disk deposition apparatus prepares two carbon protective film formation chambers (CVD chambers) to form a carbon protective film. In one carbon protective film formation chamber, carbon protective film formation (deposition) is performed. During that time, in the other carbon protective film formation chamber, a carbon film deposited on its exposed inner surface is removed by ashing using oxygen plasma. This process is alternately repeated for each carrier for a substrate, thereby preventing particle generation without lowering the productivity (e.g., Japanese Patent Laid-Open Nos. 2002-133650 and 11-229150).
Another method is also adopted, which prepares at least three carbon protective film formation chambers and controls carrier transportation so as to always make one of the carbon protective film formation chambers perform ashing, aiming at further improving the productivity. Use of this method allows not only to improve the productivity but also to shorten the time of replacing a process gas to be used for carbon protective film formation with a process gas to be used for ashing (e.g., Japanese Patent Laid-Open No. 2002-25047).
The conventional information recording disk deposition apparatus prepares two or three carbon protective film formation chambers (CVD chambers) to form a carbon protective film. Ashing is performed in one of the chambers while carbon protective film deposition is performed in a remaining chamber. This enables to form a carbon protective film with few particles while ensuring the productivity.
However, when two carbon protective film formation chambers are used, replacement of the process gas for carbon protective film formation with that for ashing takes time.
Using three or more carbon protective film formation chambers makes it possible to improve the productivity as compared to the composition using two carbon protective film formation chambers and also shorten the time of replacing the process gas for carbon protective film formation with that for ashing. However, since the number of carbon protective film formation chambers increases, the apparatus becomes bulky (the apparatus installation area increases), and expensive. Additionally, it is necessary to sequentially change the chamber without the carrier among the three or more carbon protective film formation chambers, resulting in very complex carrier transportation control.
As a problem common to the composition with two carbon protective film formation chambers and the composition with three or more chambers, immediately after the process has changed from ashing to plasma CVD, the atmosphere in the chamber is not stable yet, and the characteristics of a carbon protective film formed on a substrate at that time are poor.
Normally, for example, 25 substrates in one cassette are supplied to the apparatus. Hence, a demand has arisen for processing substrates in a single cassette in the same carbon protective film formation chamber for substrate quality management. In the conventional methods, however, such a process is impossible because the chamber used for carbon protective film formation changes for each substrate.